Gas separation is useful in many industries and can typically be accomplished by flowing a mixture of gases over an adsorbent material that preferentially adsorbs one or more gas components while not adsorbing one or more other gas components. The non-adsorbed components are recovered as a separate product.
One particular type of gas separation technology is swing adsorption, such as temperature swing adsorption (TSA), pressure swing adsorption (PSA), partial pressure swing adsorption (PPSA), rapid cycle temperature swing adsorption (RCTSA), rapid cycle pressure swing adsorption (RCPSA), rapid cycle partial pressure swing adsorption (RCPPSA), and not limited to but also combinations of the fore mentioned processes, such as pressure and temperature swing adsorption. As an example, PSA processes rely on the phenomenon of gases being more readily adsorbed within the pore structure or free volume of an adsorbent material when the gas is under pressure. That is, the higher the gas pressure, the greater the amount of readily-adsorbed gas adsorbed. When the pressure is reduced, the adsorbed component is released, or desorbed from the adsorbent material.
The swing adsorption processes (e.g., PSA and/or TSA) may be used to separate gases of a gas mixture because different gases tend to fill the micropore of the adsorbent material to different extents. For example, if a gas mixture, such as natural gas, is passed under pressure through a vessel containing an adsorbent material that is more selective towards carbon dioxide than it is for methane, at least a portion of the carbon dioxide is selectively adsorbed by the adsorbent material, and the gas exiting the vessel is enriched in methane. When the adsorbent material reaches the end of its capacity to adsorb carbon dioxide, it is regenerated by reducing the pressure, thereby releasing the adsorbed carbon dioxide. Then, the adsorbent material is typically purged and repressurized prior to starting another adsorption cycle.
The swing adsorption processes typically involve adsorbent bed units, which include adsorbent beds disposed within a housing and configured to maintain fluids at various pressures for different steps in a cycle within the unit. These adsorbent bed units utilize different packing material in the bed structures. For example, the adsorbent bed units utilize checker brick, pebble beds or other available packing. As an enhancement, some adsorbent bed units may utilize engineered packing within the bed structure. The engineered packing may include a material provided in a specific configuration, such as a honeycomb, ceramic forms or the like.
Further, various adsorbent bed units may be coupled together with conduits and valves to manage the flow of fluids through the cycle. Orchestrating these adsorbent bed units involves coordinating the steps in the cycle for each of the adsorbent bed units with other adsorbent bed units in the system. A complete cycle can vary from seconds to minutes as it transfers a plurality of gaseous streams through one or more of the adsorbent bed units.
As may be appreciated, the removal of contaminants may result in the process operating in different modes, such as a startup mode and a normal operation mode. The startup mode may be utilized to prepare the equipment (e.g., the adsorbent bed and various stream) for the normal operation mode. The normal operation mode may be utilized when the process is receiving various streams, such as the gaseous feed stream, and removing contaminants from the gaseous feed stream to provide a product stream, which may be referred to as steady state. For example, the conventional processes may operate in normal operation mode to treat hydrocarbon containing streams containing water (H2O) or carbon dioxide (CO2) to prepare the stream for downstream processing, such as natural gas liquid recovery (NGL) or liquefied natural gas (LNG) processing. The normal operation modes may be different for each of the respective downstream processes based on the respective specifications that are involved for normal operational mode. For example, a typical LNG specification requires the CO2 content to be less than 50 parts per million molar (ppm).
During the startup mode, the cycle may be different than the cycle utilized for normal operation mode. Conventional systems may utilize a single heating step to regenerate the adsorbent material with high temperatures to remove any contaminants as the startup mode cycle. For example, a startup process involving a mole sieve unit may include heating the bed to temperatures in excess of 550° F.
Unfortunately, conventional startup mode processes have certain limitations. For example, the process in startup mode may involve merely heating the adsorbent material to high temperatures. The heating of the adsorbent material to high temperatures in the conventional approaches typically rely upon dedicated high-temperature startup heaters. These heaters are expensive, involve large capital expenditure and high operational costs. In addition, these heaters increase the weight and footprint of the facility. Further, the cycle time is typically longer than necessary to remove contaminants to ensure sufficient time is provided for downstream equipment to begin operations. In addition, the temperature that the adsorbent material are exposed to may lessen the operational life of the adsorbent material and may lessen the efficiency of the adsorbent material.
Accordingly, there remains a need in the industry for apparatus, methods, and systems that provided enhancements to the start-up processes associated with hydrocarbon recovery processes. In particular, a need exists for enhancements to startup mode processes for rapid cycle swing adsorption processes.